PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: At least 4 weeks since prior antineoplastic chemotherapy Endocrine therapy: See Disease Characteristics Stable dose of dexamethasone for at least 72 hours prior to catheter placement Radiotherapy: See Disease Characteristics No prior radiosurgery boost (e.g., gamma knife or stereotactic radiosurgery) At least 8 weeks since prior radiotherapy Surgery: See Disease Characteristics At least 4 weeks since prior craniotomy